The Sith Empire, also known as the Great Sith Empire, the Old Sith Empire or the Ancient Order, was a wealthy and powerful empire established by the first dark Jedis who were banished from the Old Jedi Order.
The Empire existed for two thousand years before their final war against the growing Galactic Republic, which was known as the Hundred-Year Darkness.
The Jedi exiles fled to the remote planet of Korriban, where, after conquering it, they began a long period of building and expansion. The Dark Jedi became known as the Sith Order, and they developed an Empire in complete isolation for two thousand years before it was eventually discovered by the Republic during the Great Expansion.
The Empire invaded many Republican settlements over this century, but eventually it was defeated. The Sith Empire was believed to have been destroyed by Republic forces during the second battle of Korriban.
Though the Sith Empire was defeated, it served as an example to be followed by numerous Empires of later eras, with a legacy that extended across millennia. The Sith Order survived in both the Outer Rim Territories and the Unknown Regions, leading the way for one Sith Lord, Palpatine, to ultimately destroy the Old Republic in 20 BBY and create a new Sith Empire, which despite his best efforts, could never live up to the power and greatness the ancient Empire possessed